U.S. patent number 4,870,831 [Application Number 07/305,906] was granted by the patent office on 1989-10-03 for multi-type air conditioner system with oil level control for parallel operated compressor therein.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Manabu Kitamoto.
United States Patent |
4,870,831 |
Kitamoto |
October 3, 1989 |
Multi-type air conditioner system with oil level control for
parallel operated compressor therein
Abstract
An outdoor unit has at least two variable-capability compressors
and has an outdoor heat exchanger coupled to the compressors having
lubricating oil supplying sections coupled together by an
oil-balancing member. A plurality of indoor units are each coupled
to the outdoor unit for forming a refrigerating cycle and each have
at least an indoor heat exchanger and an output section for
outputting demand capability data according to an air conditioning
load of the indoor heat exchanger. In accordance with the demand
capability data, a controller generates a parallel operation
command for parallel operation involving both of the compressors of
the outdoor unit with capability according to a sum of the demand
capability data from the indoor units. The parallel operation
command is executed by repeating a normal operation command for
performing a normal operation over a given time and first and
second oil-balancing operation commands for every given cycle, the
first and second oil-balancing operation commands for effecting
first and second oil-balancing operations having a mutually
complimentary relation in preceding and succeeding stages of the
normal operation.
Inventors: |
Kitamoto; Manabu (Fuji,
JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
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Family
ID: |
27286079 |
Appl.
No.: |
07/305,906 |
Filed: |
February 2, 1989 |
Foreign Application Priority Data
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Feb 9, 1988 [JP] |
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63-28112 |
Feb 9, 1988 [JP] |
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63-28115 |
Feb 10, 1988 [JP] |
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63-29277 |
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Current U.S.
Class: |
62/84; 62/193;
62/175; 417/3 |
Current CPC
Class: |
F24F
3/065 (20130101); F25B 49/022 (20130101); F25B
31/002 (20130101); F25B 2400/075 (20130101); Y02B
30/70 (20130101); F25B 13/00 (20130101); F25B
2600/021 (20130101) |
Current International
Class: |
F25B
49/02 (20060101); F25B 31/00 (20060101); F24F
3/06 (20060101); F25B 13/00 (20060101); F25B
039/04 () |
Field of
Search: |
;62/84,193,228.4,175,230
;417/3 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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61-205754 |
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Sep 1986 |
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JP |
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62-87770 |
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Apr 1987 |
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JP |
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62-102046 |
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May 1987 |
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JP |
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Primary Examiner: Wayner; William E.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
What is claimed is:
1. An air conditioner comprising:
an outdoor unit having at least two variable-capability compressors
and an outdoor heat exchanger coupled to said compressors having
lubricating oil supplying sections coupled together by an
oil-balancing member;
a plurality of indoor units each coupled to said outdoor unit for
forming a refrigerating cycle and each having at least an indoor
heat exchanger and means for outputting demand capability data
according to an air conditioning load of said indoor heat
exchanger; and
control means for generating, in accordance with said demand
capability data, a parallel operation command for parallel
operation involving both of said compressors of said outdoor unit
with capability according to a sum of said demand capability data
from said indoor units, said parallel operation command being a
repetition of a normal operation command for performing a normal
operation over a given time and first and second oil-balancing
operation commands for every given cycle, said first and second
oil-balancing operation commands for effecting first and second
oil-balancing operations having a mutually complimentary relation
in preceding and succeeding stages of said normal operation.
2. The air conditioner according to claim 1, wherein said normal
operation command permits an operation with substantially a same,
given capability by both of said two variable-capability
compressors.
3. The air conditioner according to claim 1, wherein said first
oil-balancing operation command permits one of said two
variable-capability compressors to be driven at alternate higher
and lower capabilities than that of the other compressor for a
given time.
4. The air conditioner according to claim 3, wherein said second
oil-balancing operation command permits said two
variable-capability compressors to be driven in a capability
relation opposite to that involved in said first oil-balancing
operation command.
5. The air conditioner according to claim 1, wherein said normal
operation command permits an alternate execute of a first operation
in which said two variable-capability compressors have
substantially a same given, capability and a second operation in
which a given capability difference is provided between said
compressors.
6. The air conditioner according to claim 5, wherein said first
oil-balancing operation command permits an operation without said
given capability difference for a given time when said second
operation by said normal operation command is executed, and then
permits said two variable-capability compressors to be driven with
said capability of one of said compressor being set higher and
lower than that of the other compressor over a given time.
7. The air conditioner according to claim 6, wherein said second
oil-balancing operation command permits an operation without said
given capability difference for a given time when said second
operation by said normal operation command is executed, and then
permits said two variable-capability compressors to be driven with
a capability relation being set opposite to that brought by said
first oil-balancing operation command.
8. The air conditioner according to claim 1, wherein said means for
outputting said demand capability in each of said plurality of
indoor units includes detecting means for detecting an air
conditioning load of said indoor heat exchanger.
9. The air conditioner according to claim 1, further comprising a
branch unit for providing parallel connection between said outdoor
unit and said plurality of indoor units to form respective
refrigerating cycles, and having a plurality of cooling medium flow
rate controlling means for refrigerating cycles.
10. The air conditioner according to claim 9, further comprising
second control means for supplying a control command to each of
said cooling medium flow rate controlling means of said branch unit
in accordance with demand capability data from said plurality of
indoor units, and outputting sum data of each of said demand
capability data.
11. The air conditioner according to claim 1, wherein said two
variable-capability compressors are coupled in parallel to each
other through check valves provided on cooling medium outlet sides
thereof.
12. The air conditioner according to claim 1, wherein said said
outdoor unit further has a four-way valve, a parallel arrangement
of a heating expansion valve, a check valve for forming a cooling
cycle, a liquid tank and an accumulator.
13. The air conditioner according to claim 9, wherein said branch
unit further has parallel arrangements each having a plurality of
cooling heat expansion valves, and a plurality of gas side opening
valves.
14. The air conditioner according to claim 11, wherein said outdoor
unit further has oil separators provided between cooling medium
outlet sides of said two variable-capability compressors and said
check valves, and oil bypass means provided to extend from said oil
separators to cooling medium inlet sides of said compressors.
15. The air conditioner according to claim 1, wherein said
oil-balancing member of said outdoor unit has an oil-balancing pipe
for providing communication between bottom sections of said two
variable-capability compressors.
16. The air conditioner according to claim 8, wherein said
detecting means has an operation section for setting an indoor
temperature, a temperature sensor for detecting an indoor
temperature, and an indoor controller for computing a difference
between said temperature set through said operation section and
said temperature detected by said temperature sensor and outputting
said demand capability data corresponding to said temperature
difference.
17. The air conditioner according to claim 10, wherein said second
control means serves as a multicontroller in said branch unit.
18. The air conditioner according to claim 1, wherein said control
means is provided as an indoor controller in said outdoor unit.
19. The air conditioner according to claim 18, wherein said outdoor
controller comprises a microcomputer and peripheral circuits and is
coupled to motors of said two variable-capability compressors
through two inverters externally coupled to said outdoor
controller.
20. The air conditioner according to claim 19, wherein said demand
capability data and said sum data are output operational frequency
setting signals for output operation.
21. An air conditioner comprising:
an outdoor unit having two inverters for supplying a drive output
of a given operational frequency, two compressor motors driven with
a variable speed in response to reception of said drive outputs of
said two inverters, at least two variable-capability compressors
coupled to said two compressor motors, and an outdoor heat
exchanger coupled to said compressors having lubricating oil
supplying sections coupled together by an oil-balancing member;
a plurality of indoor units each coupled to said outdoor unit for
forming a refrigerating cycle and each having at least an indoor
heat exchanger and means for outputting demand capability data
according to an air conditioning load of said indoor heat
exchanger; and
first control means for controlling output operation frequencies
from said two inverters of said outdoor unit in accordance with
said demand capability data from said plurality of indoor
units;
second control means for cyclically performing an oil-balancing
operation for providing a given difference between said output
operational frequencies from said two inverters during parallel
operation of said two variable-capability compressors of said
outdoor unit;
third control means for independently detecting input currents to
said two inverters of said outdoor unit and for, when a detection
result is greater or equal to a given value, effecting a current
release for reducing an output operational frequencies from a
corresponding one of said inverters, by priority over said
oil-balancing operation by said second control means; and
fourth control means for, when said current release to said one of
said inverters is effected by said third control means, controlling
said output operational frequency from the other inverter to be
equal to a reduced output operational frequency of said one of said
inverters.
22. The air conditioner according to claim 21, wherein said means
for outputting said demand capability in each of said plurality of
indoor units includes detecting means for detecting an air
conditioning load of said indoor heat exchanger.
23. The air conditioner according to claim 21, further comprising a
branch unit for providing parallel connection between said outdoor
unit and said plurality of indoor units to form respective
refrigerating cycles, and having a plurality of cooling medium flow
rate controlling means for refrigerating cycles.
24. The air conditioner according to claim 23, further comprising
fifth control means for supplying a control command to each of said
cooling medium flow rate controlling means of said branch unit in
accordance with demand capability data from said plurality of
indoor units, and outputting sum data of each of said demand
capability data.
25. The air conditioner according to claim 21, wherein said two
variable-capability compressors are coupled in parallel to each
other through check valves provided on cooling medium outlet sides
thereof.
26. The air conditioner according to claim 21, wherein said said
outdoor unit further has a four-way valve, a parallel arrangement
of a heating expansion valve, a check valve for forming a cooling
cycle, a liquid tank and an accumulator.
27. The air conditioner according to claim 23, wherein said branch
unit further has parallel arrangements each having a plurality of
cooling heat expansion valves, and a plurality of gas side opening
valves.
28. The air conditioner according to claim 10, wherein said fifth
control means serves as a multicontroller in said branch unit.
29. The air conditioner according to claim 21, wherein said first
through fourth control means include a section serving as an
outdoor controller in said outdoor unit.
30. A method for controlling an air conditioner comprising an
outdoor unit having at least two variable-capability compressors
and a plurality of indoor units, said method comprising the steps
of:
controlling a quantity of said compressors in operation and
operational frequencies thereof in accordance with demand
capabilities of said indoor units;
carrying out a normal operation for driving both of said
compressors at substantially a same operational frequency during
parallel operation of said compressors; and
executing an oil-balancing operation by repeating, over a given
cycle, a first oil-balancing operation in which said operational
frequency of one of said compressors is set to be higher or lower
than that of the other compressor for a given time while
maintaining said operational frequency of said other compressor at
a given operational frequency to thereby execute an oil-balancing
operation through an oil-balancing pipe provided between said
compressors, and a second oil-balancing operation in which an
oil-balancing operation is executed by setting a relation of
operation frequencies of said compressors opposite to that involved
in said first oil-balancing operation.
31. A method for controlling an air conditioner comprising an
outdoor unit having at least two variable-capability compressors
and a plurality of indoor units, said method comprising the steps
of:
controlling a quantity of said compressors in operation and
operational frequencies thereof in accordance with demand
capability of said indoor units;
controlling a net capability of said compressors by combining a
first drive mode for driving both of said compressors at
substantially a same operational frequency during parallel
operation of said compressors and a second drive mode for driving
said compressors with a given frequency difference being provided
between said operational frequencies of said compressors;
executing a first oil-balancing operation in which first both of
said compressors are driven at substantially a same operation
frequency and are then driven with the operational frequency of one
of said compressors being set higher and lower for a given time
than that of the other compressor; and
executing a second oil-balancing operation in which said first
oil-balancing operation is executed by setting a relation of
operational frequencies of said compressors opposite to that
involved in said first oil-balancing operation.
32. A method for controlling an air conditioner comprising an
outdoor unit having at least two variable-capability compressors
and two inverter circuits for supplying a drive power to said
compressors, and a plurality of indoor units, said method
comprising the steps of:
controlling output frequencies of said two inverter circuits in
accordance with a sum of demand capabilities of said indoor
units;
cyclically performing an oil-balancing operation to provide a given
difference between said output frequencies of said inverter
circuits during parallel operation of said compressors;
detecting an incoming current to said inverter circuits;
executing a current release for reducing said output frequency of
that inverter circuit whose incoming current is detected in said
current detecting step to have exceeded a set value, to a given
value; and
setting said output frequency of said other inverter circuit to
said given value at a time a current release is effected.
Description
RELATED APPLICATION
The subject matter of the present invention is generally related to
the subject matter of the following U.S. applications:
______________________________________ Application No. Filed Name
of Applicant ______________________________________ 07/225,483 July
28, 1988 Kitamoto Clt. Ref: Not yet filed Unknown EKI-63P1090-1
______________________________________
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multi-type air conditioner
system with an oil level control for parallel operating compressors
and, more particularly, to an air conditioner system having a
heat-pump type refrigerating cycle, which includes an outdoor unit
having at least two variable-capability compressors and a plurality
of indoor units.
2. Description of the Related Art
In general, the above multi-type air conditioner system performs a
single-compressor operation involving one of the compressors of the
outdoor unit or a parallel operation involving two compressors in
accordance with a demand capability of each indoor unit.
The outdoor unit has two variable-capability compressors and two
inverter circuits for supplying drive power to these compressors.
This outdoor unit is coupled with a branching unit to which a
plurality of indoor units are coupled.
With the above design, the individual indoor units send to the
branching unit their respective frequency setting signals
representing their demand capabilities according to their air
conditioning loads. The branching unit acquires the demand
capabilities of the individual indoor units from the received
frequency setting signals and sends a sum frequency setting signal
corresponding to the sum of the demand capabilities, to the outdoor
unit. In accordance with the received sum frequency setting signal,
the outdoor unit controls the output frequency of each inverter
circuit to fulfill the capability requested by each indoor
unit.
The present inventors have already disclosed an invention which
contributes to an improvement of this type of air conditioner
system, in U.S. patent application Ser. No. 225,483, entitled
"Multi-Type Air Conditioner System With Starting Control For
Parallel Operated Compressor Therein" and filed on July 28, 1988,
Great Britain Patent Application No. 8818016.1 and filed on July
25, 1988, Australian Patent Application No. 19792/88. The disclosed
invention is concerned with a technique for smooth execution of the
above mentioned parallel operation and improvement of oil-balancing
effect.
The technique for improving the oil-balancing effect is to provide
an oil return passage in the individual compressors having their
base sections coupled to each other by an oil-balancing pipe,
thereby preventing the undesired locking of the compressors which
may be caused by dry-out of the oil.
This technique disclosed in the earlier application is particularly
effective in a case where two compressors have the exact (maximum)
capability. In practice, however, no two compressors are exactly
the same so that their capabilities, though specified to be the
same, should differ from each other in strict sense. It is often
the case that two compressors having a significant difference in
their (maximum) capabilities are combined in the aforementioned air
conditioner system, a combination of three-horse power (HP) type
and five-horse power (HP) type, for example.
It is therefore necessary to further improve the oil-balancing
effect which could be provided by the technique used in the earlier
application.
As will be described later, using a large-diameter oil-balancing
pipe can provide an oil-balancing effect that copes with the
difference in capabilities of two compressors. In this case,
however, there would arise a problem of generating undesired
vibration or noise that is transmitted to each compressor through
the large-diameter oil-balancing pipe. This problem is likely to
deteriorate the mechanical strength of this pipe and thus damage or
break it at the worst, which is crucial to the air conditioner
system in terms of reliability.
In this respect, therefore, it is necessary to consider some means
to prevent adverse influence on current release from being caused
by the aforementioned improvement of the oil-balancing effect.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a new and
improved multi-type air conditioner system with an oil level
control for parallel operating compressors therein, which system
can provide an oil-balancing effect between compressors without
using a large-diameter oil-balancing pipe to thereby prevent
transmission of compressor vibration or compressor noise to indoor
units, can ensure a sufficient strength of an oil-balancing pipe
and has a high reliability.
It is another object of this invention to provide an air
conditioner system which, in addition to the above features, can
further improve the oil-balancing effect.
It is a further object of this invention to provide an air
conditioner system which can surely execute oil-balancing operation
without any influence of a current release operation to thereby
always ensure a stable operation.
According to one aspect of this invention, there is provided an air
conditioner comprising:
an outdoor unit having at least two variable-capability compressors
and an outdoor heat exchanger coupled to the compressors having
lubricating oil supplying sections coupled together by an
oil-balancing member;
a plurality of indoor units each coupled to the outdoor unit for
forming a refrigerating cycle and each having at least an indoor
heat exchanger and means for outputting demand capability data
according to an air conditioning load of the indoor heat exchanger;
and
control means for generating, in accordance with the demand
capability data, a parallel operation command for parallel
operation involving both of the compressors of the outdoor unit
with capability according to a sum of the demand capability data
from the indoor units, the parallel operation command being a
repetition of a normal operation command for performing a normal
operation over a given time and first and second oil-balancing
operation commands for every given cycle, the first and second
oil-balancing operation commands for effecting first and second
oil-balancing operations having a mutually complimentary relation
in preceding and succeeding stages of the normal operation.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of the present invention
should be understood from the following detailed description of
preferred embodiments with reference to the accompanying drawings
in which:
FIGS. 1 through 6 illustrate the first embodiment of this
invention;
FIG. 1 being a schematic diagram illustrating the general
refrigerating cycle within an air conditioner,
FIG. 2 being a schematic diagram illustrating the relation between
each compressor and an oil-balancing pipe,
FIG. 3 being a schematic diagram illustrating the structure of a
refrigerating cycle,
FIG. 4 being a characteristic diagram illustrating the state of an
operational frequency changing at the time of oil-balancing
operation,
FIG. 5 being a schematic diagram illustrating the changing state of
an oil level in a case where the operational frequency of the first
compressor shown in FIG. 5 is set lower than that of the second
compressor, and
FIG. 6 being a schematic diagram illustrating the changing state of
an oil level in a case where the operational frequency of the first
compressor is set higher than that of the second compressor,
FIG. 7 is a characteristic diagram illustrating a change in the
operational frequency at the time of oil-balancing operation
according to the second embodiment;
FIG. 8 is a diagram illustrating a specific example of an indoor
controller and its peripheral circuits according to the third
embodiment; and
FIG. 9 is a diagram illustrating the relation between a detected
current and a set value according to the third embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
To begin with the first embodiment of this invention will be
described below with reference to FIGS. 1 through 6. The same
reference numerals as given in FIG. 1 are used in FIGS. 2 to 6 to
specify identical or corresponding components for omission of their
description.
FIG. 1 illustrates a heat-pump type refrigerating cycle to which
the multi-type air conditioner system embodying this invention is
applied.
In FIG. 1, reference numeral A denotes an outdoor unit, B denotes a
branching unit, and C, D and E denote indoor units. Outdoor unit A
is equipped with two variable-capability compressors 1 and 2 which
are coupled in parallel via check valves 3 and 4, respectively. A
heat-pump type refrigerating cycle is formed through compressors 1
and 2, a four-way valve 5, a parallel arrangement of an outdoor
heat exchanger 6, a heating expansion valve 7 and a check valve 8
for forming a cooling cycle, a liquid tank 9, electrically-powered
flow rate control valves 11, 21 and 31, a parallel arrangement of
cooling expansion valves 12, 22 and 32 and check valves 13, 23 and
33 for forming a heating cycle, indoor heat exchangers 14, 24 and
34, gas-side opening valves (electromagnetic opening valves) 15, 25
and 35, and an accumulator 10.
Cooling expansion valves 12, 22 and 32 respectively have
heat-sensing tubes 12a, 22a and 32a attached to gas-side cooling
medium pipes of indoor heat exchangers 14, 24 and 34.
In other words, indoor heat exchangers 14, 24 and 34 are arranged
in parallel to pass a cooling medium in the direction of the
illustrated solid arrows at the time of a cooling operation, to
thereby form a cooling cycle, and this arrangement passes a cooling
medium in the direction of the illustrated, broken arrows at the
time of a heating operation through a switching operation executed
by four-way valve 5, to thereby form a heating cycle.
In such an air conditioner system, the quantity of compressors 1
and 2 in operation and their capabilities are controlled to provide
the demand capability of each indoor unit and the opening of flow
rate control valves 11, 21 and 31 are controlled to adjust the rate
of the cooling medium flowing in each indoor heat exchanger.
Expansion valves 12, 22 and 32 serve to maintain a constant heat
application to the cooling medium irrespective of a change in the
flow rate of the cooling medium, thus ensuring a stable and
efficient operation.
When the demand capability of each indoor unit increases at the
time of, for example, a cooling operation, therefore, the
capability of compressor 1 may be increased or compressor 2 may
even be driven in addition to compressor 1. When the demand
capability of each indoor unit decreases in this state, the
capability of compressor 2 may be reduced or, compressor 2 may even
be stopped, leaving only compressor 1 being driven.
With the above arrangement alone, however, the amount of a
lubricating oil outgoing from compressors 1 and 2 and the amount of
the oil returning thereto are not exactly the same, so that the
amount of the lubricating oil in one compressor increases with time
while that in the other compressor decreases. This causes imbalance
of the oil quantity between these compressors and thus makes it
difficult to ensure a stable operation.
Further, when the level of the lubricating oil falls below a oil
level limit (operatable level), the supply of the lubricating oil
to a lubricating section is stopped, which may damage compressors 1
and 2.
To overcome the possible unbalanced amounts of oil in compressors 1
and 2, it is proposed in the aforementioned earlier application to
connect these compressors by an oil-balancing pipe so that the
lubricating oil can flow from the one containing a larger amount of
oil to the other with less oil.
Since the capabilities of the individual compressors 1 and 2 are
not exactly the same, the one with a larger capability would have a
larger pressure loss in an oil inlet pipe and have a smaller
pressure within the compressor casing. This tendency is prominent
if compressors 1 and 2 have different capacities.
As a result, the cooling medium gas flows through the oil-balancing
pipe to the compressor having a lower internal casing pressure from
the other having a higher internal casing pressure, and the
lubricating oil flows in the same direction accordingly.
When the amount of the lubricating oil returning to the latter
compressor with a higher internal casing pressure is greater than
the amount of the oil outgoing therefrom, the lubricating oil above
the oil-balancing pipe moves through the pipe to the compressor
with a lower internal casing pressure. Accordingly, the oil levels
in the individual compressors become equal to each other at the
position of the oil-balancing pipe. On the other hand, when the
amount of the returning oil is smaller than the amount of the
outgoing oil, the oil level in the compressor with a higher
internal casing pressure decreases with time below the oil level
limit. In this case, the lubricating oil in the compressor with a
lower internal casing pressure is interrupted from going to the
compressor with a lower internal casing pressure due to this
difference in internal casing pressure.
In this respect, therefore, an oil-balancing pipe with a wide oil
passage may be used as mentioned earlier to balance the oil levels
in compressors 1 and 2 as well as to set a balanced internal casing
pressure in both compressors.
However, the use of a large-diameter oil-balancing pipe makes it
easier to transmit the vibration generated in one compressor to the
other so that resonance or the like may occur depending on a
combination of the operational frequencies of both compressors 1
and 2. This may result in compressor vibration or compressor noise
and may damage the oil-balancing pipe.
In other words, if compressors 1 and 2 are connected to each other
simply by an oil-balancing pipe, the lubricating oil in the casing
of the compressor having a higher internal casing pressure flows
through the pipe to the other one having a lower internal casing
pressure due to the difference in this pressure which is caused by
a difference in capability of the compressors, thus imbalancing the
oil levels in the casings of the compressors. If an oil-balancing
pipe with a wide oil passage is used to balance the oil levels in
compressors 1 and 2 as well as to set a balanced internal casing
pressure in both compressors, it becomes easier to transmit the
vibration generated in one compressor to the other so that
resonance or the like may occur depending on a combination of the
operational frequencies of both compressors 1 and 2. This may
result in compressor vibration or compressor noise and may damage
the oil-balancing pipe as well.
With the above in mind, the air conditioner system according to the
first embodiment of this invention is designed to perform such a
control as to repeat the following operations for a given cycle T
(for example, T=15 min.) during a parallel operation of both
compressors. The operations include a normal operation for driving
both compressors at substantially the same operational frequency
over a given time t.sub.0 (for example, t.sub.0 =12 min.), a first
oil-balancing operation, which follows the normal operation and
drives one of the compressors at alternate higher and lower
operational frequencies than the operational frequency of the other
compressor for every given times t.sub.1 and t.sub.2 (for example,
t.sub.1 =t.sub.2 =90 sec.) while maintaining the operational
frequency of the latter compressor at a predetermined level, a
second oil-balancing operation, which drives the compressors with
the relation of their operational frequencies involved in the first
oil-balancing operation being reversed after the normal operation
is carried out following the first oil-balancing operation.
In short, the air conditioner system with the above design repeats
the normal operation, first oil-balancing operation and second
oil-balancing operation for a given cycle during parallel operation
of the compressors. Under the first and second oil-balancing
operations, the operational frequencies of these compressors are
changed, one higher than the other, so that the lubricating oil in
the casings of both compressors can efficiently flow through the
oil-balancing pipe. Therefore, this air conditioner system can
provide oil-balancing effect between the individual compressors
without employing a large-diameter oil-balancing pipe and can
prevent generation of compressor vibration and compressor
noise.
The above control will now be described more specifically. As shown
in FIG. 1, an oil separator 41 is provided to a cooling medium
outlet pipe of compressor 1, and an oil bypass pipe 42 is provided
to extend from the separator 41 to a cooling medium inlet pipe of
compressor 1.
Further, an oil separator 43 is provided to a cooling medium outlet
pipe of compressor 2, and an oil bypass pipe 44 is provided to
extend from the separator 43 to a cooling medium inlet pipe of
compressor 2.
Casings 1a and 2a of compressors 1 and 2 are connected to
communicate with each other by means of an oil-balancing pipe 45,
as shown in FIG. 2. In this case, compressors 1 and 2 are disposed
in the same plane. Compressors 1 and 2 are set in advance with the
proper reference oil level and the allowable minimum oil level for
the lubricating oil retained within casings 1a and 2a; pipe 45 is
mounted at substantially the same height as the reference oil
level. Diameter of pipe 45 is 12.7 mm, for example, in both
combination of 3 HP and 5 HP or 5 HP and 5 HP types
compressors.
FIG. 3 illustrates a controller for a refrigerating cycle. In this
diagram, reference numeral 50 denotes an outdoor controller mounted
in outdoor unit A. This outdoor controller 50 comprises a
microcomputer and its peripheral circuits and has its outputs
coupled to inverter circuits 51 and 52. Inverter circuits 51 and 52
rectify the voltage from an AC power source 53, convert the
resultant voltages into AC voltages with given frequencies in
accordance with a command from outdoor controller 50, and supply
the converted voltages as drive power to compressor motors 1M and
2M, respectively.
Reference numeral 60 denotes a multi-controller mounted in
branching unit B. This multi-controller 60 comprises a
microcomputer and its peripheral circuits and has its outputs
coupled to flow rate control valves 11, 21 and 31 and opening
valves 15, 25 and 35.
Reference numerals 70, 80 and 90 denote indoor controllers mounted
respectively in indoor units C, D and E. These indoor controllers
70, 80 and 90 each comprise a microcomputer and its peripheral
circuits and are coupled to operation sections 71, 81 and 91 and
indoor temperature sensors 72, 82 and 92, respectively.
The individual indoor controllers 70, 80 and 90 send frequency
setting signals f.sub.1, f.sub.2 and f.sub.3 as demand capabilities
to multi-controller 60. Multi-controller 60 in turn acquires the
sum of the demand capabilities of the individual indoor units C, D
and E from the received frequency setting signals and sends a
frequency setting signal f.sub.0 corresponding to the sum to
outdoor controller 50 as controlled capability.
Note that the multi-controller is described in detail in U.S. Pat.
No. 4,720,982 assigned to the present applicant. This description
is incorporated herein.
The operation of thus constructed air conditioner system will be
described below.
Assume now that all the indoor units are performing a cooling
operation.
At this time, indoor controller 70 of indoor unit C calculates the
difference between the temperature detected by indoor temperature
sensor 72 and the temperature set through operation section 71 and
sends the frequency setting signal f.sub.1 corresponding to the
temperature difference to multi-controller 60 as the requested
cooling capability. Similarly, indoor controllers 80 and 90 of
indoor units D and E send the frequency setting signals f.sub.2 and
f.sub.3 as the requested cooling capabilities to multi-controller
60.
Based on the received frequency setting signals, multi-controller
60 attains the sum of the requested cooling capabilities of the
individual indoor units C, D and E, and sends the frequency setting
signal f.sub.0 corresponding to the acquired sum to outdoor
controller 50. Based on the received frequency setting signal
f.sub.0, outdoor controller 50 acquires the sum of the requested
cooling capabilities of indoor units C, D and E, and controls the
quantity of compressors 1 and 2 in operation and the operational
frequency F (output frequencies of inverter circuits 51 and 52). In
this case, as the sum of the requested cooling capabilities
increases, outdoor controller 50 changes a single-compressor
operation involving compressor 1 to a parallel operation involving
both compressors 1 and 2.
During operation of compressor 1, most of the lubricating oil
included in the pumped out cooling medium is collected by oil
separator 41 and is returned to compressor 1 through oil bypass
pipe 42. Similarly, during operation of compressor 2, most of the
lubricating oil included in the pumped out cooling medium is
collected by oil separator 43 and is returned to compressor 2
through oil bypass pipe 44. That cooling medium which has not been
collected circulates through the refrigerating cycle and returns to
compressors 1 and 2.
Multi-controller 60 controls the openings of flow rate control
valves 11, 21 and 31 in accordance with the frequency setting
signals from indoor units C, D and E, so that the proper amounts of
the cooling medium corresponding to the requested cooling
capabilities of these indoor units C, D and E will flow through
indoor heat exchangers 14, 24 and 34, respectively. In addition,
expansion valves 12, 22 and 32 control the heat application to the
cooling medium in the respective indoor heat exchangers 14, 24 and
34 at a predetermined level.
Outdoor controller 50 performs such a control as to repeat the
following three operations for a given cycle T during a parallel
operation of both compressors 1 and 2:
(1) The normal operation for driving both compressors 1 and 2 at
substantially the same operational frequency over a given time
T-(t.sub.1 +t.sub.2).
(2) The first oil-balancing operation which follows the normal
operation and drives one of compressors, for example, 1, at
alternate higher and lower operational frequencies Fa than the
operational frequency Fb of the other compressor 2 for every given
times t.sub.1 and t.sub.2 while maintaining the operational
frequency Fb of the latter compressor 2 at a predetermined
frequency Fb.sub.0.
(3) The second oil-balancing operation which drives compressors 1
and 2 with the relation of their operational frequencies involved
in the first oil-balancing operation being reversed after the
normal operation is carried out following the first oil-balancing
operation.
Referring now to FIGS. 4 through 6, a description will be given of
the oil-balancing operation of compressors 1 and 2. FIG. 4
illustrates a change in operational frequency Fa of one compressor
1 (which is illustrated by the solid line in FIG. 4) and a change
in operational frequency Fb of the other compressor 2 (which is
illustrated by the broken line) in the oil-balancing operation.
Suppose that compressors 1 and 2 are driven in the normal operation
mode with their operational frequencies Fa and Fb being set at
substantially the same value (i.e., Fa.sub.O .apprxeq.Fb.sub.O
=56.4 Hz, for example), and the first oil-balancing operation is
executed after a given time T-(t.sub.1 +t.sub.2) is elapsed in this
normal operation.
At the time of the first oil-balancing operation, first, the
operational frequency Fa of one compressor 1 is reduced by n step
frequencies over time t.sub.1. In this case, the operational
frequency Fb of the other compressor 2 is maintained at Fb.sub.0.
Accordingly, the operational frequency Fa.sub.1 of compressor 1
becomes lower than the operational frequency Fb.sub.0 of compressor
2. As a result, the internal casing pressure Pa of compressor 1
gets higher than the internal casing pressure Pb of compressor 2,
so that the lubricating oil in the casing of high-pressure-side
compressor 1 gradually flows together with the cooling medium in
the casing of low-pressure-side compressor 2 through pipe 45. This
gradually lowers the oil level within the casing of compressor 1
and gradually increases the oil level within the casing of
compressor 2, as shown in FIG. 5. The lower limit of the oil level
in the casing of compressor 1 is the bottom line of pipe 45 in this
case.
When time t.sub.1 elapses with the operational frequency Fa of
compressor 1 being reduced to Fa.sub.1 (=31.1 Hz for example), this
frequency Fa is increased by n step frequencies from Fa.sub.0 over
time t.sub.2. In this case, the operational frequency Fb of the
other compressor 2 is maintained at Fb.sub.0. Accordingly, the
operational frequency Fa.sub.2 (=90 Hz, for example) of compressor
1 becomes higher than the operational frequency Fb.sub.0 of
compressor 2. As a result, the internal casing pressure Pa of
compressor 1 gets lower than the internal casing pressure Pb of
compressor 2, so that the lubricating oil in the casing of
high-pressure-side compressor 2 gradually flows together with the
cooling medium in the casing of low-pressure-side compressor 1
through pipe 45. This gradually lowers the oil level within the
casing of compressor 2 and gradually increases the oil level within
the casing of compressor 1, as shown in FIG. 6.
When time t.sub.2 elapses with the operational frequency Fa of
compressor 1 being increased to Fa.sub.2, the first oil-balancing
operation is completed at this moment, and the operation is
returned to the normal operation with this frequency Fa being set
back to Fa.sub.0. In the normal operation region (II) after
completing the first oil-balancing operation, therefore, the oil
level in the casing of compressor 1 is kept higher than that in the
casing of compressor 2, as shown in FIG. 6. The second
oil-balancing operation is performed after a given time T-(t.sub.1
+t.sub.2) elapses in this normal operation mode.
At the time of the second oil-balancing operation, first, the
operational frequency Fb of compressor 2 is reduced by n step
frequencies (n=6, for example) over time t.sub.1. In this case, the
operational frequency Fa of compressor 1 is maintained at Fa.sub.0.
Accordingly, the operational frequency Fb.sub.1 (=31.1 Hz, for
example) of compressor 2 becomes lower than the operational
frequency Fa.sub.0 of compressor 1. As a result, the internal
casing pressure Pb of compressor 2 gets higher than the internal
casing pressure Pa of compressor 1, so that the lubricating oil in
the casing of high-pressure-side compressor 2 gradually flows
together with the cooling medium in the casing of low-pressure-side
compressor 1 through pipe 45. This gradually lowers the oil level
within the casing of compressor 2 and gradually increases the oil
level within the casing of compressor 1, as shown in FIG. 6.
When time t.sub.1 elapses with the operational frequency Fb of
compressor 2 being reduced to Fb.sub.1, this frequency Fb is
increased by n step frequencies (n=6, for example) from Fb.sub.0
over time t.sub.2. In this case, the operational frequency Fa of
compressor 1 is maintained at Fa.sub.0. Accordingly, the
operational frequency Fb.sub.2 (=90 Hz, for example) of compressor
2 becomes higher than the operational frequency Fa.sub.0 of
compressor 1. As a result, the internal casing pressure Pb of
compressor 2 gets lower than the internal casing pressure Pa of
compressor 1, so that the lubricating oil in the casing of
high-pressure-side compressor 1 gradually flows together with the
cooling medium in the casing of low-pressure-side compressor 2
through pipe 45. This gradually lowers the oil level within the
casing of compressor 1 and gradually increases the oil level within
the casing of compressor 2, as shown in FIG. 5.
When time t.sub.2 elapses with the operational frequency Fb of
compressor 2 being increased to Fb.sub.2, the operation is returned
to the normal operation at this moment, with this frequency Fb
being set back to Fb.sub.0. In the normal operation region (I)
after completing the second oil-balancing operation, therefore, the
oil level in the casing of compressor 2 is kept higher than that in
the casing of compressor 1, as shown in FIG. 5. Thereafter, the
normal operation and the first oil-balancing operation or the
second oil-balancing operation are alternately repeated for a given
time period.
The air conditioner system with the above structure therefore
performs such a control as to repeat the following three operations
for a given cycle T during a parallel operation of both compressors
1 and 2:
(1) The normal operation for driving both compressors 1 and 2 at
substantially the same operational frequency over a given time
t.sub.0.
(2) The first oil-balancing operation which follows the normal
operation and drives one of compressors, for example, 1, at
alternate higher and lower operational frequencies Fa than the
operational frequency Fb of the other compressor 2 for every given
times t.sub.1 and t.sub.2 while maintaining the operational
frequency Fb of the latter compressor 2 at a predetermined
frequency Fb.sub.0.
(3) The second oil-balancing operation which drives compressors 1
and 2 with the relation of their operational frequencies involved
in the first oil-balancing operation being reversed after the
normal operation is carried out following the first oil-balancing
operation.
Accordingly, it is possible to alternately switch the oil level
statuses in compressors 1 and 2 in the normal operation range (II)
after completion of the first oil-balancing operation and those in
the normal operation range (I) after completion of the second
oil-balancing operation from one to the other. Therefore, in a
long-run operation, it is possible to prevent the oil level in one
compressor from being imbalanced with respect to the other, thereby
ensuring balanced oil levels in these compressors 1 and 2.
It is therefore possible to always ensure a stable operation and
prevent the dry out of oil in compressors 1 and 2 or the locking of
the compressors, which would result in preventing compressors 1 and
2 from being damaged due to such undesired phenomenon.
Further, oil-balancing pipe 45 need not have a large diameter and
thus can keep a sufficient mechanical strength, resulting in
avoidance of compressor vibration or compressor noise and making
the system cost-effective.
In addition, the oil-balancing effect can be realized without
particularly providing expensive float type regulators and level
sensors in compressors 1 and 2, so that the overall system
arrangement can be simplified, thus resulting in reduction of
manufacturing cost.
Furthermore, during the oil-balancing operation of compressors 1
and 2, the operation for reducing the operational frequency to a
level lower by n step frequencies than Fa.sub.0 (or Fb.sub.0) in
the normal operation and the operation of increasing the
operational frequency to be higher by n step frequencies than
Fa.sub.0 (or Fb.sub.0) are alternately executed. During this
oil-balancing operation, an abnormality in the output current of
inverter circuit 51 (or 52) is discriminated at the time the
operational frequency is increased by n step frequencies than
Fa.sub.0 (or Fb.sub.0) in the normal operation for current release.
Even if a current release for reducing the output frequency of
inverter circuit 51 (or 52) to a given value is executed to thereby
disable the oil-balancing operation at an increasing frequency, it
is possible to surely execute the oil-balancing operation at the
time the operational frequency is reduced by n step frequencies
than Fa.sub.0 (or Fb.sub.0) in the normal operation, in accordance
with the discrimination result. Accordingly, an oil-balancing
operation can be executed at least once for each time T to thereby
provide the oil-balancing effect.
Even if both of the operational frequencies Fa and Fb of
compressors 1 and 2 reach the maximum values, it is possible to
surely execute the oil-balancing operation at the time the
operational frequency is reduced by n step frequencies than
Fa.sub.0 (or Fb.sub.0) in the normal operation. Accordingly, an
oil-balancing operation can be executed at least once for each time
T to thereby provide the oil-balancing effect.
Even if both of the operational frequencies Fa and Fb of
compressors 1 and 2 reach the minimum values, it is possible to
surely execute the oil-balancing operation at the time the
operational frequency is increased by n step frequencies than
Fa.sub.0 (or Fb.sub.0) in the normal operation. Accordingly, an
oil-balancing operation can be executed at least once for each time
T to thereby provide the oil-balancing effect.
This invention is in no way restricted to the above embodiment. For
instance, although the above description of the embodiment has been
given with reference to the case where three indoor units are
employed, this invention can similarly apply to a case with more
than three or only two indoor units. This invention can of course
be modified in various manners within the scope and spirit of the
invention.
As described above, the air conditioner system according to the
first embodiment of this invention is designed such that an
oil-balancing pipe is provided between the individual compressors
and that the following operations are repeated for a given cycle T
during a parallel operation of both compressors.
(1) The normal operation for driving both compressors at
substantially the same operational frequency over a given time
t.sub.0 during their parallel operation.
(2) The first oil-balancing operation which follows the normal
operation and drives one of the compressors at alternate higher and
lower operational frequencies than the operational frequency of the
other compressor for every given times t.sub.1 and t.sub.2 while
maintaining the operational frequency of the latter compressor at a
predetermined level.
(3) The second oil-balancing operation which drives the compressors
with the relation of their operational frequencies involved in the
first oil-balancing operation being reversed after the normal
operation is carried out following the first oil-balancing
operation.
With this design, the present air conditioner system can provide an
oil-balancing effect between the individual compressors without
using a large-diameter oil-balancing pipe, thus preventing
generation of compressor vibration and compressor noise as well as
providing the oil-balancing pipe with a sufficiently high
mechanical strength. This can contribute to improving the
reliability of the system.
The second embodiment of this invention will now be described.
The air conditioner system according to the second embodiment of
this invention operates as follows. During parallel operation of
both compressors, a normal operation for controlling the net
capability of both compressors is executed over a given time
t.sub.0 ; this control is done by combination of the first drive
mode in which both compressors are driven at substantially the same
operational frequency, and the second drive mode in which the
compressors are driven with a predetermined difference given in
operational frequencies of the compressors. After this normal
operation, the first oil-balancing operation is performed which
first drives both compressors at substantially the same operational
frequency over a given time t and drives one of the compressors at
alternate higher and lower operational frequencies for every given
times t.sub.1 and t.sub.2 with respect to the other compressor
while maintaining the operational frequency of the latter
compressor at a predetermined level. The second oil-balancing
operation which drives the compressors with the relation of their
operational frequencies involved in the first oil-balancing
operation being reversed after the normal operation following the
first oil-balancing operation has been carried out.
The air conditioner system according to the second embodiment can
improve the resolution of the net capability of both compressors by
controlling the combination of the first drive mode for driving
both compressors in parallel operation at substantially the same
operational frequency in the normal operation and the second drive
mode for driving the compressors with a given difference in their
operational frequencies. In addition, during the oil-balancing
operation, both compressors are first driven at substantially the
same operational frequency and then one of them is driven at
alternate higher and lower operational frequencies than that of the
other compressor for each given time period while maintaining the
operational frequency of the latter compressor at a constant level.
This prevents the oil-balancing operation from being executed while
both compressors are driven in the second drive mode. Further, the
second oil-balancing operation is repeated for every given cycle
before and after the first oil-balancing operation is executed.
Under the first and second oil-balancing operations, the
operational frequencies of these compressors are changed, one
higher than the other, so that the lubricating oil in the casings
of both compressors can efficiently flow through the oil-balancing
pipe. Therefore, this air conditioner system can provide
oil-balancing effect between the individual compressors without
employing a large-diameter oil-balancing pipe and can prevent
generation of compressor vibration and compressor noise.
The second embodiment has the same structure as the first
embodiment shown in FIGS. 1 through 3, and its operation is the
same as that of the first embodiment except for operation
(frequency) control and oil-balancing (operation) control for
compressors 1 and 2 which are executed by outdoor controller 50 (to
be described later).
According to the second embodiment, outdoor controller 50 controls
the net capability of two compressors 1 and 2 in parallel operation
by combining the first drive mode for driving both compressors 1
and 2 at substantially the same operational frequency in the normal
operation and the second drive mode for driving the compressors
with a given difference in their operational frequencies. Suppose
that compressors 1 and 2 are driven with the operational frequency
Fa of one compressor 1 being set to Fa.sub.0 and the operational
frequency Fb of the other one being set to Fb.sub.0 (Fa.sub.0
=Fb.sub.0) (first drive mode). In this mode, let us assume that the
net of demand capabilities of individual indoor units C, D and E is
sequentially increased. First, the operational frequency Fa of
compressor 1 is increased to Fa.sub.0 +.DELTA.F and the operational
frequency Fb of compressor 2 is maintained at Fb.sub.0 to provide a
given frequency difference therebetween, and both compressors are
driven under this condition (second drive mode). Then, after both
compressors are driven for a given time under the above condition,
the operational frequency Fb of compressor 2 is increased to
Fb.sub.0 +.DELTA.F, the operational frequency Fa of compressor 1 is
maintained at Fa.sub.0 +.DELTA.F, and both compressors are driven
at the same operational frequency for a given time under this
condition (first drive mode). Further, similarly, the operational
frequency Fa of compressor 1 is increased to Fa.sub.0 +2.DELTA.F,
the operational frequency Fb of compressor 2 is maintained at
Fb.sub.0 +.DELTA.F to provide a given frequency difference
therebetween, and both compressors are driven for a given time
under this condition (second drive mode). Subsequently, the
operational frequency Fb of compressor 2 is increased to Fb.sub.0
+2.DELTA.F, the operational frequency Fa of compressor 1 is
maintained at Fa.sub.0 +2.DELTA.F, and both compressors are driven
at the same operational frequency for a given time (first drive
mode). The net capability of both compressors 1 and 2 is controlled
to come to the state which corresponds to the sum of the demand
capabilities of indoor units C, D and E by alternately repeating
the first and second drive modes. Accordingly, the resolution of
the net capability of compressors 1 and 2 can be improved as
compared with the case where the operational frequencies Fa and Fb
of both compressors 1 and 2 are changed at the same time as the net
capability of compressors 1 and 2 is changed. It is therefore
possible to finely control the net capability of compressors 1 and
2 in accordance with a change in the sum of the demand capabilities
of indoor units C, D and E, thereby improving the operational
efficiency of both compressors 1 and 2 and the pleasantness.
Outdoor controller 50 performs oil-balancing (operation) control to
balance the amounts of the lubricating oil in the casings of
compressors 1 and 2 during their parallel operation.
Referring now to FIG. 7, a description will be given of the
oil-balancing operation of compressors 1 and 2. FIG. 7 illustrates
a change in operational frequency Fa of one of the compressor, 1,
(which is illustrated by the solid line in FIG. 7) and a change in
operational frequency Fb of the other compressor 2 (which is
illustrated by the broken line) in the oil-balancing operation.
Suppose that compressors 1 and 2 are driven in the normal operation
mode (in which the first and second drive modes are alternately
repeated), and are operating in the second drive mode. For
descriptive simplification, however, FIG. 7 shows the normal
operation being carried out only in the second drive mode. Let us
assume that the operational frequency Fa of compressor 1 is set at
Fa1 and operational frequency Fb of compressor 2 is set at Fb.sub.0
Fb.sub.0 =Fb.sub.0 ; Fa.sub.1 =Fa.sub.0 +.DELTA.F>Fb.sub.0), as
shown in FIG. 7. Then, the first oil-balancing operation is
executed after a given time t.sub.0 elapses under this
condition.
In the first oil-balancing operation, the operational frequency Fa
of compressor 1 is decreased to Fa.sub.0 from Fa.sub.1 first, and
both compressors 1 and 2 are driven at substantially the same
operational frequency (operational frequency Fa being Fa.sub.0 and
operational frequency Fb being Fb.sub.0) for a given time t (t=10
sec., for example). Then, the operational frequency Fa of one
compressor 1 is reduced by n step frequencies over time t.sub.1. In
this case, the operational frequency Fb of the other compressor 2
is maintained at Fb.sub.0. Accordingly, the operational frequency
Fa.sub.2 of compressor 1 becomes lower than the operational
frequency Fb.sub.0 of compressor 2. As a result, the internal
casing pressure Pa of compressor 1 gets higher than the internal
casing pressure Pb of compressor 2, so that the lubricating oil in
the casing of high-pressure-side compressor 1 gradually flows
together with the cooling medium in the casing of low-pressure-side
compressor 2 through pipe 45. This gradually lowers the oil level
within the casing of compressor 1 and gradually increases the oil
level within the casing of compressor 2, as shown in FIG. 5. The
lower limit of the oil level in the casing of compressor 1 is the
bottom line of pipe 45 in this case.
When time t.sub.1 elapses with the operational frequency Fa of
compressor 1 being reduced to Fa.sub.2, this frequency Fa is
increased by n step frequencies from Fa.sub.0 over time t.sub.2. In
this case, the operational frequency Fb of the other compressor 2
is maintained at Fb.sub.0. Accordingly, the operational frequency
Fa.sub.3 of compressor 1 becomes higher than the operational
frequency Fb.sub.0 of compressor 2. As a result, the internal
casing pressure Pa of compressor 1 gets lower than the internal
casing pressure Pb of compressor 2, so that the lubricating oil in
the casing of high-pressure-side compressor 2 gradually flows
together with the cooling medium in the casing of low-pressure-side
compressor 1 through pipe 45. This gradually lowers the oil level
within the casing of compressor 2 and gradually increases the oil
level within the casing of compressor 1, as shown in FIG. 6.
When time t.sub.2 elapses with the operational frequency Fa of
compressor 1 being increased to Fa.sub.3, the first oil-balancing
operation is completed at this moment, and the operation is
returned to the normal operation with this frequency Fa being set
back to Fa.sub.1. In the normal operation region after completing
the first oil-balancing operation, therefore, the oil level in the
casing of compressor 1 is kept higher than that in the casing of
compressor 2, as shown in FIG. 6. When a given time t0 elapses in
this normal operation mode, the operation is performed with the
relation of the operational frequencies of both compressors 1 and 2
being reversed (second oil-balancing operation).
At the time of the second oil-balancing operation, first, the
operational frequency Fa of compressor 1 is decreased to Fa.sub.0
from Fa.sub.1 first, and both compressors 1 and 2 are driven at
substantially the same operational frequency (operational frequency
Fa being Fa.sub.0 and operational frequency Fb being Fb.sub.0) for
a given time t. Then, the operational frequency Fb of compressor 2
is reduced by n step frequencies over time t.sub.1. In this case,
the operational frequency Fa of compressor 1 is maintained at
Fa.sub.0. Accordingly, the operational frequency Fb.sub.2 of
compressor 2 becomes lower than the operational frequency Fa.sub.0
of compressor 1. As a result, the internal casing pressure Pb of
compressor 2 gets higher than the internal casing pressure Pa of
compressor 1, so that the lubricating oil in the casing of
high-pressure-side compressor 2 gradually flows together with the
cooling medium in the casing of low-pressure-side compressor 1
through pipe 45. This gradually lowers the oil level within the
casing of compressor 2 and gradually increases the oil level within
the casing of compressor 1, as shown in FIG. 6.
When time t.sub.1 elapses with the operational frequency Fb of
compressor 2 being reduced to Fb.sub.2, this frequency Fb is
increased by n step frequencies from Fb.sub.0 over time t.sub.2. In
this case, the operational frequency Fa of compressor 1 is
maintained at Fa.sub.0. Accordingly, the operational frequency
Fb.sub.3 of compressor 2 becomes higher than the operational
frequency Fa.sub.0 of compressor 1. As a result, the internal
casing pressure Pb of compressor 2 gets lower than the internal
casing pressure Pa of compressor 1, so that the lubricating oil in
the casing of high-pressure-side compressor 1 gradually flows
together with the cooling medium in the casing of low-pressure-side
compressor 2 through pipe 45. This gradually lowers the oil level
within the casing of compressor 1 and gradually increases the oil
level within the casing of compressor 2, as shown in FIG. 5.
When time t.sub.2 elapses with the operational frequency Fb of
compressor 2 being increased to Fb.sub.3, the operation is returned
to the normal operation at this moment, with this frequency Fb
being set back to Fb.sub.0 while setting back the operational
frequency Fa of 1 compressor 1 to Fa.sub.1. In the normal operation
region after completing the second oil-balancing operation,
therefore, the oil level in the casing of compressor 2 is kept
higher than that in the casing of compressor 1, as shown in FIG. 5.
Thereafter, the normal operation and the first oil-balancing
operation or the second oil-balancing operation are alternately
repeated for a given time period T.
The air conditioner system with the above structure therefore
performs such a control as to repeat the following operations for a
given cycle during a parallel operation of both compressors 1 and
2:
(1) The first oil-balancing operation which follows the normal
operation and drives one of compressors, for example, 1, at
alternate higher and lower operational frequencies Fa than the
operational frequency Fb of the other compressor 2 for every given
times t.sub.1 and t.sub.2 while maintaining the operational
frequency Fb of the latter compressor 2 at a predetermined
frequency Fb.sub.0.
(2) The second oil-balancing operation which drives compressors 1
and 2 with the relation of their operational frequencies involved
in the first oil-balancing operation being reversed after the
normal operation is carried out following the first oil-balancing
operation.
Accordingly, it is possible to alternately switch the oil level
statuses in compressors 1 and 2 in the normal operation range after
completion of the first oil-balancing operation and those in the
normal operation range after completion of the second oil-balancing
operation from one to the other.
According to the second embodiment, therefore, the following
advantages can be obtained in addition to various advantages
attained by the first embodiment.
The air conditioner system according to the second embodiment can
improve the resolution of the net capability of both compressors 1
and 2 by controlling the combination of the first drive mode for
driving both compressors 1 and 2 in parallel operation at
substantially the same operational frequency (Fa.sub.0
.apprxeq.Fb.sub.0) in the normal operation and the second drive
mode for driving the compressors with a given difference .DELTA.F
in their operational frequencies.
Further, according to the second embodiment, during the
oil-balancing operation, both compressors 1 and 2 are first driven
at substantially the same operational frequency (Fa.sub.0
.apprxeq.Fb.sub.0) and then one of them is driven at alternate
higher and lower operational frequencies than that of the other
compressor. This prevents the oil-balancing operation from being
executed while both compressors are driven in the second drive
mode. It is therefore possible to surely prevent the difference
.DELTA.F of the operational frequencies of compressors 1 and 2 in
the oil-balancing operation from being imbalanced when the
oil-balancing operation has started with both compressors 1 and 2
being driven in the second drive mode. In other words, an
oil-balancing effect can be attained even when the operation
advances to the oil-balancing operation with compressors 1 and 2
both being in the second drive mode.
The air conditioner system according to the second embodiment of
this invention operates as follows. During parallel operation of
both compressors, a normal operation for controlling the net
capability of both compressors is executed over a given time
t.sub.0 ; this control is done by combination of the first drive
mode in which both compressors are driven at substantially the same
operational frequency, and the second drive mode in which the
compressors are driven with a predetermined difference given in
operational frequencies of the compressors. After this normal
operation, the first oil-balancing operation is performed which
first drives both compressors at substantially the same operational
frequency over a given time t and drives one of the compressors at
alternate higher and lower operational frequencies for every given
times t.sub.1 and t.sub.2 with respect to the other compressor
while maintaining the operational frequency of the latter
compressor at a predetermined level. The second oil-balancing
operation which drives the compressors with the relation of their
operational frequencies involved in the first oil-balancing
operation being reversed after the normal operation following the
first oil-balancing operation has been carried out.
The air conditioner system according to the second embodiment can
provide an oil-balancing effect between the individual compressors
without using a large-diameter oil-balancing pipe, thus preventing
generation of compressor vibration and compressor noise as well as
providing the oil-balancing pipe with a sufficiently high
mechanical strength. This can contribute to improving the
reliability of the system.
The third embodiment of this invention will now be described.
The first and second embodiments basically cyclically perform the
oil-balancing operation to provide a given difference between the
output frequencies of the individual inverter circuits during
parallel operation of the individual compressors to overcome an
unbalance in the refrigerating oil (lubricating oil) in the
individual compressors, thereby protecting the compressors.
Although there is not a significant difference between the output
frequencies of the individual inverter circuits during parallel
operation of two compressors, the current release can independently
function for each inverter circuit. When a current release
functions for either one of the inverter circuits, therefore, there
would cause a significant difference between the output frequencies
of the inverter circuits. Further, this difference may result from
various conditions such as a difference in capability or capacity
(horse power) of the individual compressors or the current release
functioning simultaneously for the individual inverter
circuits.
Since the current release has a priority over the oil-balancing
operation, it may interrupt the oil-balancing operation, thus
making the proper transition to frequency control after the current
release difficult. This would result in an improper oil-balancing
effect.
To ensure an oil-balancing operation free of the influence of the
current release, therefore, the air conditioner system according to
the third embodiment comprises:
two inverter circuits for supplying drive power to individual
compressors;
means for controlling the output frequencies of these inverter
circuits in accordance with the sum of the demand capabilities of
the individual indoor units;
means for cyclically performing an oil-balancing operation to
provide a given difference between the output frequencies of the
inverter circuits during parallel operation of the compressors;
current detecting means for detecting an incoming current to the
inverter circuits;
current release means for reducing the output frequency of that
inverter circuit whose incoming current is detected to exceed a set
value, to a given value; and
means for setting the output frequency of the other inverter
circuit to the given value at the time a current release is
effected.
With the above arrangement, when the input current to an inverter
circuit exceeds a set value, a current release is executed so that
the output frequency of that inverter circuit is reduced by a given
value. At this time, the output frequency of the other inverter
circuit is set at the same value to eliminate a possible difference
between the output frequencies of the individual inverter
circuits.
The third embodiment basically has the same structure and function
as the first embodiment shown in FIGS. 1 through 3, but differs
therefrom only in the current release function added to outdoor
controller 50 (to be described later).
FIG. 8 illustrates a specific example of outdoor controller 50 and
its peripheral units as used in the third embodiment.
Outdoor controller 50 comprises a microcomputer 100 serving as a
main unit, inverter microcomputers 101 and 102 for driving and
controlling inverters and inverter drivers 103 and 104.
Inverter circuits 51 and 52 respectively have current detectors 111
and 112 that serve to detect input currents. The detection outputs
of these current detectors 111 and 112 are supplied to inverter
microcomputers 101 and 102.
Microcomputer 100 sends a command corresponding to the frequency
setting signal f.sub.0 from branching unit B, to inverter
microcomputers 101 and 102 and detects the output frequencies of
inverter circuits 51 and 52 by means of return signals from these
inverter microcomputers 101 and 102.
Inverter microcomputers 101 and 102 controls inverter drivers 103
and 104 in accordance with a command from microcomputer 100 and
discriminates the output frequencies of inverter circuits 51 and 52
from the detection currents from current detectors 111 and 112.
Inverter microcomputers 101 and 102 then return the discrimination
results to microcomputer 100. When the detection currents from
current detectors 111 and 112 exceed a set value, microcomputer 100
discriminates the event as an abnormal input current. Microcomputer
100 then performs a current release control to reduce the output
frequency of the associated inverter circuit to a given value and
other control such that the output frequency of the other inverter
circuit is set equal to that of the former inverter circuit.
Inverter drivers 103 and 104 render the switching elements of
inverter circuits 51 and 52 ON and OFF to provide AC voltages with
a predetermined frequency from these inverter circuits 51 and
52.
The operation of thus constructed air conditioner system will be
described below.
Assume now that all the indoor units are performing a cooling
operation.
At this time, as described earlier, indoor controller 70 of indoor
unit C calculates the difference between the temperature detected
by indoor temperature sensor 72 and the temperature set through
operation section 71 and sends the frequency setting signal f.sub.1
corresponding to the temperature difference to multicontroller 60
as the requested cooling capability (see FIGS. 1 and 3).
Similarly, indoor controllers 80 and 90 of indoor units D and E
send the frequency setting signals f.sub.2 and f.sub.3 as the
requested cooling capabilities to multicontroller 60.
Based on the received frequency setting signals, multi-controller
60 attains the sum of the requested cooling capabilities of the
individual indoor units and sends the frequency setting signal f0
corresponding to the acquired sum to outdoor controller 50.
Based on the received frequency setting signal f.sub.0, outdoor
controller 50 controls the quantity of compressors 1 and 2 in
operation and the operational frequency (output frequencies of
inverter circuits 51 and 52).
In this case, as the sum of the requested cooling capabilities
increases, outdoor controller 50 changes a single-compressor
operation involving compressor 1 to a parallel operation involving
both compressors 1 and 2.
Multi-controller 60 controls the openings of flow rate control
valves 11, 21 and 31 in accordance with the requested cooling
capabilities from indoor units C, D and E, so that the proper
amounts of the cooling medium flowing to indoor heat exchangers 14,
24 and 34, respectively to maintain the heat application to the
cooling medium at a constant level.
During parallel operation of two compressors 1 and 2, outdoor
controller 50 cyclically performs the oil-balancing operation.
In this oil-balancing operation, for example, the output frequency
of inverter circuit 51 is set to a command frequency (based on the
sum of the requested cooling capabilities) and the output frequency
of inverter circuit 52 is vertically changed within a given range
around the set value so as to provide a given difference between
the output frequencies of inverter circuits 51 and 52.
In this case, when the output frequency of inverter circuit 51 gets
higher than that of inverter circuit 52, the casing pressure of
compressor 1 becomes lower than the casing pressure of compressor
2, thus making it easier for the refrigerating oil in compressor 2
to flow to compressor 1 through pipe 45. On the other hand, when
the output frequency of inverter circuit 52 gets higher than that
of inverter circuit 51, the casing pressure of compressor 2 becomes
lower than the casing pressure of compressor 1, thus making it
easier for the refrigerating oil in compressor 1 to flow to
compressor 2 through pipe 45.
After this oil-balancing operation is executed over a given time
based on the count of an internal timer of microcomputer 100, the
output frequencies of 51 and 52 are set to the command frequency
and the normal operation will be returned.
Inverter microcomputers 101 and 102 of outdoor controller 50 shown
in FIG. 8 monitor the detection currents from current detectors 111
and 112; when the detection current reaches the P region exceeding
the set value I2 shown in FIG. 9, microcomputers 101 and 102
discriminate the event as an abnormal input current.
When the abnormal input current to inverter circuit 51 is detected,
the output frequency of inverter circuit 51 is reduced by a given
amount to perform the current release. This reduction in frequency
is executed by priority irrespective of the aforementioned
oil-balancing operation being in progress, and it is done for each
reception of the detection current until this current falls off the
P region. When the detection current falls to the Q region between
I.sub.1 and I.sub.2, the output frequency of inverter circuit 51 is
retained as it is. When the detection current further falls down to
the 0 region below I.sub.1, the current release is stopped and the
output frequency is set at the command frequency.
At this time, microcomputer 100 compares the content (command
frequency) of a command to inverter microcomputer 101 with the
content of a return signal from this inverter microcomputer 101
(i.e., the output frequency of inverter circuit 51). When these
contents differ from each other, microcomputer 100 detects that the
current release has been effected in inverter circuit 51, and
immediately sets the output frequency of inverter circuit 52
through inverter microcomputer 101 to the same value as the output
frequency of inverter circuit 51.
Similarly, with regard to an abnormal input current to inverter
circuit 52, a current release for reducing the output frequency of
this inverter circuit 52 executed. At the same time, the output
frequency of inverter circuit 51 is set to be equal to the output
frequency of inverter circuit 52.
Further, when abnormal input currents are simultaneously supplied
to inverter circuits 51 and 52, the current release is executed for
both the inverter circuits 51 and 52. In this case, microcomputer
101 compares the reduced output frequencies of inverter circuits 51
and 52 and sets the higher output frequency to equal to the lower
one.
In this manner, the current release is executed in at least one of
inverter circuits 51 and 52. The output frequency of the other
inverter circuit is set to that of the inverter circuit undergoing
the current release. Accordingly, even when the current release
interrupts the oil-balancing operation, transition to the frequency
control after the current release can be easily and smoothly
carried out by eliminating a difference between the output
frequencies of the individual inverter circuits. It is therefore
possible to surely execute the oil-balancing operation without
adverse influence from the current release, thus preventing a
so-called dry out of oil in compressors 1 and 2 and ensuring a
constant, stable operation with a high efficiency.
Since compressors 1 and 2 are provided with an oil bypass passage
such as an oil separator, the refrigerating oil can be efficiently
collected.
The above description of the third embodiment have been given with
reference only to a cooling operation, but this invention can also
apply to a heating operation to produce the same effects.
Although the above description discusses the case involving three
indoor units, this invention can deal with more than three or only
two indoor units easily.
It should be noted that this invention is in no way restricted to
the above particular embodiment, but can be modified in various
manners without departing from its scope.
As described above, the air conditioner system according to the
third embodiment comprises two inverter circuits for supplying
drive power to individual compressors; means for controlling the
output frequencies of these inverter circuits in accordance with
the sum of the demand capabilities of the individual indoor units;
means for cyclically performing an oil-balancing operation to
provide a given difference between the output frequencies of the
inverter circuits during parallel operation of the compressors;
current detecting means for detecting an incoming current to the
inverter circuits; current release means for reducing the output
frequency of that inverter circuit whose incoming current is
detected to exceed a set value, to a given value; and means for
setting the output frequency of the other inverter circuit to the
given value at the time a current release is effected. This air
conditioner system according to this embodiment can therefore
surely carry out the oil-balancing operation without adverse
influence of execution of a current release, thereby ensuring a
constant, stable operation.
* * * * *